Streptokinase immobilized covalently onto nylon and implanted subcutaneously into a rabbit has been shown to retain its activity in increasing the blood clotting time for more than 150 days. No adverse side effects in the animal were noted during this period and no evidence indicating an immune response was found. This suggests that immobilized streptokinase may be useful in the prevention of thromboembolic disorders. We plan therefore to investigate the action of immobilized streptokinase on a more quantitative basis. We hope to establish a dose response curve as well as an in vivo half-life of the immobilized enzyme. We will also investigate the long-range effects of an implantation of immobilized streptokinase on various blood factors, including levels of fibrinogen, fibrin degradation products, plasminogen, plasmin, prothrombin, the platelet count and the extent of euglobulin lysis. In addition, a careful analysis for a possible immune response will be performed. We also intend to evaluate the ability of immobilized streptokinase to prevent thrombus formation by artifically inducing thrombi in animals carrying an implant and in control animals. Similarly we hope to evaluate the ability of immobilized streptokinase to dissolve existing blood clots. Our results will aid in the evaluation of the usefulness of immobilized streptokinase in the prevention and treatment of thromboembolic disorders.